The purpose of this research was to assess the effects of exposure to selected PAHs (phenanthrene, pyrene, and fluorene) on brain acetylcholinesterase (AChE) in juvenile gilthead seabream (Sparus aurata) in short term in vivo experiments. The measured brain AChE activity was within the same range (110-200 nmol min(-1) mg prot(-1)) in all the considered treatment conditions and in the control. The only statistically significant difference in AChE activity with respect to the control group was its induction in response to the lowest tested pyrene concentration in one of two replicated studies. These results suggest that exposure to PAHs does not appreciably affect brain AChE activity.